The primary purpose of this parameter study was to carefully document occupant dynamics in well-controlled sled tests for comparison with simulated responses from the MVMA-2D analytical model. The test involved a Part 572 dummy exposed to a frontal deceleration while on a bucket seat and restrained by a lap-shoulder belt system. The length of belt webbing was incrementally increased from a snug configuration by as much as 30 cm. The addition of webbing increased the forward excursion, velocity, and acceleration of the head, chest, and hip without affecting the peak tension in the belt segments of the restraint system. Belt tension was identified as a poor measure of the horizontal load on the chest due to significant reaction forces in the lateral and vertical direction at the belt anchorages. The advanced belt system subprogram of the MVMA-2D model had to be modified to account for the influence of the lateral anchorage location on belt tensions and the planar restraint of the occupant. Although reasonable agreement was achieved in simulating the occupant dynamics, belt loads were dissimilar. The MVMA-2D model is judged to be a sophisticated, delicate tool requiring additional study and refinement.